The invention relates to apparatus for the high temperature heat treatment of pieces of material, especially ceramic material, and containing a heat treatment chamber having a number of rotating carrier elements which are arranged fixed and at least partially driven and a number of support elements which rest on the carrier elements and are transported through the heat treatment chamber with the material.
In the following description of the invention the firing of ceramic material has been selected as the sphere of application. However, the invention is not restricted to this sphere, but can also be used advantageously in the heat treatment of other material in pieces, for instance annealing and tempering of metal workpieces and in other high temperature heat treatment processes.
For firing ceramic material, roller kilns are known in which the material is conveyed through the tunnel-like kiln on a large number of rollers which are arranged in close succession one after the other. Such kilns have significant disadvantages. In order to avoid unacceptable deformation of the rollers and the ceramic material, the length and diameter of the rollers and thus, at a predetermined running speed also, the capacity of the kiln are restricted. The large number of driven rollers required results in high expenditure on equipment. Because of the necessary close arrangement of the carrier and conveyor rollers the introduction of the gaseous heating medium from above and below is uneven. Finally, glazed ceramic material cannot be fired in such roller kilns, since sticking and smearing of the rollers is unavoidable. Thus such roller kilns are severely limited in the quality of the glaze on the ceramic material to be fired.
Roller kilns are also known in which the ceramic material to be fired does not rest directly on the driven conveyor rollers but on individual carrier plates which in turn are supported on the conveyor rollers and are transported by the latter through the kiln. The size of these carrier plates corresponds to at least the surface area of the ceramic parts. A significant disadvantage of this is poor heating of the material to be fired from below and thus a generally uneven heat treatment of the ceramic material. A further disadvantage is that heating of the carrier plates to the high firing temperature as is necessary in each operation results in a very high energy consumption since the sensible heat from this auxiliary firing means cannot be recovered in practice. A further disadvantage of these known kilns is the relatively poor guiding of the carrier plates in the transport direction and the danger of the ceramic material sticking to the carrier plates.
Finally, the prior art also includes kilns in which the ceramic material to be fired rests on a number of steel wires which run parallel to one another through the tunnel-like kiln chamber and are guided at both ends of the kiln over revolving tension and transport wheels. In this kiln the relationship between the mass of the auxiliary firing means and the mass of the ceramic material and thus the energy requirement for heating the auxiliary firing means are substantially reduced; however, this known construction has further significant disadvantages. Since the wire used to support the ceramic material has no significant inherent rigidity, a plurality of support rollers must be provided and costly tensioning devices for the individual steel wires are also necessary. In view of the high mechanical and thermal stress to which the steel wires are exposed, wires are continually breaking in operation with all the disadvantageous consequences.